|The INDIRECT funtion will do that for you.|
Let's say you want to pull a value from January!C1 into Sheet13!C1.
In Sheet13!C1 enter:
=INDIRECT(A1 & "!C1")
When you enter January in A1, the formula will evaluate to
You can build formulas with INDIRECT also.
With Month Names in A1 and A2, this will multiple the values in the referenced cells:
=INDIRECT(A1&"!C2") * INDIRECT(A2&"!A2")
P.S. I would use a Drop Down to choose your month names so that typos don't screw up your formulas.
I hope that helps.